Image recording apparatus

ABSTRACT

An image recording apparatus in which an image recording material bearing an image to be recorded and an image receiving sheet are stacked together and pressurized with a pair of pressurizing rollers so that the image is transferred to the image receiving sheet. A back-up roller, the length of which is about one-third that of the pressurizing rollers, suitably presses at least one of the pressurizing rollers at the middle portion thereof.

BACKGROUND OF THE INVENTION

The present invention relates to an image recording apparatus forrecording images using photosensitive pressure-sensitive materials, andmore particularly to an image recording apparatus in which a latentimage is formed on a photosensitive pressure-sensitive image recordingmaterial by exposure, and the image recording material is pressedagainst an image receiving material for development of the image.

An example of a conventional image recording apparatus usingmicrocapsules containing a photosensitive image recording materialemploys synthetic macromolecular resin wall capsules containing a vinylcompound, photopolymerization initiator and coloring agent precursor.Such an apparatus is disclosed in commonly assigned Japanese UnexaminedPublished Patent Application No. 179836/1982. In this apparatus, themicrocapsules are hardened in the pattern of an image by opticalexposure and then pressurized so that microcapsules which were nothardened are broken to discharge the coloring agent precursor thereby toform a color image. This apparatus is advantageous in that an image ofhigh picture quality can be readily obtained by dry processing.

However, the above-described photosensitive material is disadvantageousin that it has a much lower photosensitivity than a photosensitivematerial using silver halogenides such as common photographic emulsions.

This difficulty has been eliminated by the provision of a novelphotosensitive material, as described, for example, in commonly assignedJapanese Unexamined Published Patent Application No. 275742/1986. Thisnovel photosensitive material is high in photosensitivity and providesan image high in picture quality using simple dry processing. Thephotosensitive material is formed by coating a support at least withphotosensitive silver halogenide, a reducing agent, a polymerizingcompound and a color image forming material. Of these materials, atleast the polymerizing compound and the color image forming materialare, in combination, sealed in microcapsules.

An image recording apparatus using the above-described photosensitivematerial is disclosed in Japanese Unexamined Patent Publication No.147,461/1987. In that apparatus, first the image recording material isoptically exposed to form a latent image thereon, and then subjected tothermal developing so that, in the region of the image, the polymerizingcompound is polymerized to produce macromolecular compound to therebyharden the microcapsules. Thereafter, the image recording material thusprocessed is stacked on an image receiving material having an imagereceiving layer onto which the color image forming material can betransferred, and the image recording material and the image receivingmaterial are pressurized so that, in the region where no latent image isformed, some of the microcapsules are broken to transfer the color imageforming material to the image receiving material to form a visibleimage.

In the image recording apparatus, the photosensitive material and theimage receiving material are stacked together and are then pressurizedby a pair of pressurizing rollers so that the color image formingmaterial is accurately transferred to the image receiving material. Forthis purpose, the pressurizing rollers must be sufficiently long thatthey cover the width of the photosensitive material and the imagereceiving material. Therefore, when one of the pressurizing rollers ispressed at both ends against the other, for instance by springs, the onepressurizing roller is bent so that only the two end portions of thelatter are pressed against the other pressurizing roller. That is,pressure is not sufficiently applied to the middle portion of thephotosensitive material, and accordingly the color image formingmaterial is not accurately transferred to the image receiving material.

To eliminate the above-described difficulty, an image recordingapparatus has been proposed in which a back-up roller whose middleportion is larger in diameter than the remaining two end portions isused to press only the middle portion of one of the pressurizing rollersagainst the other so that the above-described bending of thepressurizing roller is corrected. However, the image recording apparatusis still disadvantageous in that, since the large-diameter middleportion of the back-up roller tends to bend in the longitudinaldirection, only the two end portions of the large-diameter middleportion press against the pressurizing roller, as a result of which thepressure applied by the pressurizing roller is still not uniform, andhence the color image forming material is still not accuratelytransferred to the image receiving material.

Moreover, if the pressure distribution of the pressurizing rollers isnot uniform as described above, the photosensitive material and theimage receiving material have a tendency to be partially displacedtowards the part or parts of the pressurizing rollers where the pressureis lower, as a result of which the photosensitive material and the imagereceiving material are creased. The amount of creasing increases withthe amount of nonuniformity of the pressure distribution. As a result,the color image forming material is not accurately transferred to theimage receiving material, and the resultant image is considerablyirregular in density.

Also, if the pressurizing rollers' pressure distribution is not uniformas described above, the photosensitive material and the image receivingmaterial, being held by the pressurizing rollers, have a tendency to becreased. Due to the creases, the nonuniformity of the pressuredistribution is further increased, and the unevenness in density of theimage becomes more significant.

Furthermore, not only in the above-described image recording apparatus,but also in some electrophotographing apparatuses, the nip rollers areused to apply a high pressure to the image recording material to obtainthe image. In this operation, it is unavoidable that the image recordingmaterial is nonuniformly pressurized.

To eliminate the above-described difficulty, a skew roll pressurizingdevice has been proposed in which a pair of pressurizing nip rollers arearranged in such a manner that their axes form a slight angle so thatthe pressure provided in the nip region of the two rollers is uniformover their entire length. For the same purpose, a back-up rollerpressurizing device has been proposed in which two back-up rollers arearranged outside a pair of pressurizing nip rollers so that the pressureprovided in the nip region of the pressurizing nip rollers is uniformover the entire length.

However, the former device is disadvantageous in that the device cannothandle a plurality of image recording materials differing in thicknessor in width. On the other hand, when the image recording material andthe image receiving material stacked together are conveyed while beingpressurized by the pressurizing nip rollers, the image recordingmaterial and the image receiving material are conveyed in directionsperpendicular to the axes of the respective nip rollers they contact,and therefore the rear end portion of each of the image recordingmaterial and image receiving material tends to be greatly shifted fromthe front end portion in the widthwise direction.

The latter device is also disadvantageous in that, since it requires twoback-up rollers in addition to the pressurizing nip rollers, the deviceis unavoidably bulky and high in weight.

Furthermore, these two devices suffer from a difficulty that they areintricate in construction because it is necessary to adjust thepressurizing forces of the pressurizing nip rollers.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to eliminate theabove-described difficulties accompanying a conventional image recordingapparatus in which a photosensitive pressure-sensitive image recordingmaterial is optically exposed according to an image to be recorded, andthe image recording material is pressed against an image receivingmaterial so that the image is formed on the image receiving material.

More specifically, an object of the invention is to provide an imagerecording apparatus in which a photosensitive pressure-sensitive imagerecording material is optically exposed according to an image to berecorded, and the image recording material is pressed against an imagereceiving material so that the image is formed on the image receivingmaterial, and in which, when the image recording material is pressedagainst the image receiving material, the image is formed on the imagereceiving material with high picture quality.

Another object of the invention is to produce such an apparatus in whichthe weight of the apparatus can be readily reduced.

The foregoing and other objects of the invention have been achieved bythe provision of an image recording apparatus in which a photosensitivepressure-sensitive image recording material bearing an image and animage receiving material stacked together are pressurized with a pair ofpressuring rollers while being held therebetween so that the image istransferred to the image receiving material, and which, according to theinvention, comprises a back-up roller for applying a predeterminedpressurizing force to at least one of the pair of pressurizing rollersat the middle thereof, the back-up roller having a length which issubstantially one-third the length of the pair of pressurizing rollers.

The technical concept of the invention is effectively applicable to animage recording apparatus in which the image recording material isoptically exposed to form an image thereon and subjected to thermaldeveloping, and the image recording material is pressed against theimage receiving material so that the image is transferred to the latter.

A suitable image recording material has been disclosed in JapaneseUnexamined Patent Publication No. 297,742/1986. This image recordingmaterial is a photosensitive pressure-sensitive thermal-developing typeimage recording material which contains silver halogenide, a reducingagent, polymerizing compound and color image forming material. At leastthe polymerizing compound and the color image forming material are, incombination, sealed in microcapsules.

An image recording apparatus capable of using the above-describedphotosensitive pressure-sensitive thermal developing type imagerecording material has been disclosed in Japanese Unexamined PatentPublication No. 209,461/1987. In the apparatus, first the imagerecording material is optically exposed to form a latent image thereon,and is then subjected to thermal developing so that, in the region ofthe image, the polymerizing compound is polymerized to producemacromolecular compound, thereby to harden the microcapsules.Thereafter, the image receiving material is stacked on the imagerecording material thus treated, and the image receiving material andthe image recording material are pressurized so that, in the regionwhere no latent image is formed, some of the microcapsules are broken totransfer the color image forming material to the image receivingmaterial to form a visible image.

The foregoing and other objects of the invention have also been achievedby the provision of an image recording apparatus in which aphotosensitive material is employed which is formed by coating a supportwith a material which, when pressurized, fixes an image formed byoptical exposure, and a visible image is obtained by pressurization,which, according to the invention, comprises a pair of pressurizingrollers for pressurizing the photosensitive material, and a back-uproller for applying a predetermined pressure to the back of one of thepair of pressurizing rollers, the back-up roller being having acylindrical middle portion and circular-truncated-cone-shaped right andleft end portions which extend from both ends of the cylindrical middleportion and are smaller in diameter towards the outer ends thereof.

Examples of photosensitive materials which can be used in the imagerecording apparatus of this embodiment of the present invention are asfollows:

In the first example, as described above and as disclosed by commonlyassigned Japanese Unexamined Published Patent Application No.179836/1982, the photosensitive material is optically exposed so thatthe polymerizing compound is hardened according to an image to berecorded, and it is then pressurized to render the image visible. Thephotosensitive material is formed by providing a layer of syntheticmacromolecular resin wall capsules on a support which contains a vinylcompound, a photopolymerization initiator and a coloring precursor.

In the second example of the photosensitive material, a latent imageformed thereon by optical exposure is subjected to wet developing orthermal developing, and then the photosensitive material is pressurizedso that the image is made visible. Examples of such a photosensitivematerial are disclosed in Japanese Unexamined Published PatentApplication No. 53881/1986, also commonly assigned. In thephotosensitive material disclosed in the former application, afterthermal developing, the color image forming material is transferred toan image receiving material having an image receiving layer so that thedesired image is obtained. The photosensitive material is formed bycoating a support at least with photosensitive silver halogenide, areducing agent, a polymerizing compound and a color image formingmaterial. Among these materials, at least the polymerizing compound andthe color image forming material are, in combination, sealed inmicrocapsules. In the photosensitive material disclosed in the latterapplication, an image is recorded without using the image receivingmaterial; that is, it is formed on the photosensitive material itself.In other words, the image receiving layer is formed on thephotosensitive material. More specifically, a photosensitive layer isformed on a support, which layer contains silver halogenide, a reducingagent, a polymerizing compound and two types of materials which colorwhen contacted. The polymerizing compound and one of the two types ofmaterials are, in combination, sealed in microcapsules, and the other ofthe two types of materials is provided outside the microcapsules.

Another object of the invention is to provide an image recording methodusing a photosensitive material which is formed by coating a supportwith a material which, when pressurized, fixes an image formed byoptical exposure and in which the photosensitive material is conveyedsmoothly without being deformed so that an image is recorded with highpicture quality.

The foregoing and other objects of the invention have been achieved bythe provision of an image recording method in which the photosensitivematerial is pressurized and conveyed by a pair of pressurized rollers ina direction perpendicular to the longitudinal direction of thepressurizing rollers in such a manner that, while the photosensitivematerial passes through the pressurizing rollers, a pressure whichincreases gradually along the axis of the pressurizing rollers from bothends towards the middle thereof is applied to the photosensitivematerial.

A further object of the invention is to provide an image forming methodusing a photosensitive material which is formed by coating a supportwith a material, which, when pressurized, fixes an image formed byoptical exposure, in which an image is recorded with high picturequality, and a pair of pressurizing rollers for pressurizing thephotosensitive material can be manufactured at a low cost.

The foregoing and other objects of the invention have been achieved bythe provision of an image recording method in which a photosensitivematerial formed by coating a support with a material which, whenpressurized, fixes an image formed by optical exposure is employed and avisible image is obtained through pressurization, in which thephotosensitive material is pressurized and conveyed by a pair ofpressurizing rollers in a direction perpendicular to the longitudinaldirection of the pressurizing rollers in such a manner that, whilepassing through the pressuring rollers, the photosensitive material ispressed by a pressure whose distribution in the longitudinal directionof the pressurizing rollers varies by no more than 30%.

Still another object of the invention is to provide an image recordingapparatus with a pressure-operated image transferring device of simpleconstruction which provides a uniform pressure in the nipping region ofa pair of pressurizing nip rollers arranged parallel to one another,thereby to positively transfer the image on the image receivingmaterial.

The foregoing and other objects of the invention have been achieved bythe provision of an image recording apparatus employing a photosensitivematerial formed by coating a support with a material which, whenpressurized, fixes an image formed thereon through optical exposure andthe image thus fixed is transferred from the photosensitive material toan image receiving material, which, according to the invention,comprises a pressure-operated image transferring device including afixed nip roller rotatably supported which has a width (L₁) ranging from210 mm to 350 mm and a diameter (D₁) ranging from 30 mm to 50 mm; a freenip roller arranged parallel to the fixed nip roller, the free niproller having a width (L₂) equal to or larger than the width (L₁) of thefixed nip roller and a diameter (D₂) in a range of D₁ /1.6 to D₁ /1.3;and a back-up roller pushing the free nip roller against the fixed niproller, the back-up roller having an effective back-up width (L₃)defined by the following equation:

    L.sub.3 =L.sub.1 /3±10 mm

In the pressure-operated image transferring device of the invention, oneof the two parallel nip rollers is rotatably supported at both ends,while the other is movably pushed against the fixed nip roller by meansof the back-up roller. That is, the three rollers cooperate to make thepressure in the nipping region of the two nip rollers uniform over thelength. Furthermore, the pressure in the nip region can be adjustedmerely by changing the pressurizing force of the back-up roller.

The manner in which the foregoing and other objects are achieved by thisinvention will become more apparent from the following detaileddescription and the appended claims when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an explanatory diagram showing the arrangement of an exampleof an image recording apparatus according to the invention;

FIG. 2 is an explanatory diagram showing a pressurizing unit in theimage recording apparatus according to the invention;

FIG. 3 is a front view showing the arrangement of a first example of apressure-operated image transferring section in the image recordingapparatus of a first embodiment of the invention;

FIG. 4 is a characteristic diagram indicating a pressurizing forcedistribution in the image recording apparatus of FIG. 3;

FIG. 5 is a characteristic diagram indicating pressurizing force withimage density in the image recording apparatus of FIG. 3;

FIG. 6 is a front view, with parts removed, showing a second embodimentof a pressure-operated image transferring section in the image recordingapparatus of the invention;

FIG. 7 is an explanatory diagram showing the arrangement of apressurizing unit in the apparatus according to a third embodiment ofthe invention;

FIG. 8 is a front view showing the arrangement of a pressure-operatedimage transferring section in the apparatus of FIG. 7;

FIG. 9 is a characteristic diagram showing the pressure distribution ofa pair of pressurizing rollers in accordance with a fourth embodiment ofthe invention;

FIG. 10 is a characteristic diagram showing the distribution of pressureof a pair of pressurizing rollers in the apparatus in FIG. 1 inaccordance with a fifth embodiment of the invention;

FIG. 11 is a graphical representation indicating the distribution ofpressure applied to the sheets in the pressure-operated imagetransferring section shown in FIG. 8 in accordance with a sixthembodiment of the invention;

FIG. 12 is an explanatory diagram showing the arrangement of thepressurizing unit used in a seventh embodiment of an image recordingapparatus of the invention;

FIG. 13 is a front view showing the arrangement of a pressure-operatedimage transferring section in the pressurizing unit shown in FIG. 12;

FIG. 14 is a graphical representation indicating the distribution ofpressure applied to the sheets in the pressure-operated imagetransferring section shown in FIG. 13;

FIG. 15 is an explanatory diagram showing the arrangement of an exampleof an image recording apparatus according to an eighth embodiment of theinvention;

FIG. 16 is an explanatory diagram outlining a pressure-operated imagetransferring device in the image recording apparatus of FIG. 15; and

FIGS. 17A through 17B graphical representations indicating the resultsof experiments on the pressure-operated image transferring device ofFIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will be described with referenceto the accompanying drawings.

As shown in FIG. 1, an image recording apparatus 10 according to theinvention includes a housing 12 which accommodates a photosensitivematerial supplying section 13 having a photosensitive pressure-sensitivethermal-developing type recording material (hereinafter referred tomerely as "a photosensitive material" when applicable); an image readingsection 15 for reading image data provided on an original S, a thermalimage developing section 17 for heating a photosensitive material A, asheet stacking section 19 for stacking an image receiving sheet C on thephotosensitive material A, a pressure-operated image transferringsection 21 for applying pressure to the photosensitive material A andthe image receiving sheet C, a sheet separating section 23 forseparating the image receiving sheet C from the photosensitive materialA, and an image fixing section 25 for fixing the image on the imagereceiving sheet C.

A transparent supporting glass plate 14 is provided on the top surfaceof the housing 12 to support an original S. The glass plate 14 isreciprocated, as indicated by a double-headed arrow in FIG. 1, over anopening 16 by a drive device (not shown) mounted on the upper surface ofthe image reading section 15. The image reading section 15 includes alight source for irradiating the original S through the opening 16, anda focusing optical system 20. The light source 18 and the focusingoptical system 20 are surrounded by a wall 22.

The photosensitive material supplying section 13 is optically shieldedby a partition wall 26 provided in the upper portion of the housing 12.A magazine 30 including a roll of photosensitive material A is loadedinto the photosensitive material supplying section 13 through a lidmember 28 coupled to the top surface of the housing 12 in such a mannerthat the lid member 28 can be freely opened and closed. Thephotosensitive material A is formed by coating a support withphotosensitive silver halogenide, a reducing agent, a polymerizingcompound and a color image forming material. Of these materials, atleast the polymerizing compound and the color image forming material aresealed, in combination, in microcapsules.

The photosensitive material supplying section 13 has first throughfourth roller pairs 32a through 32d for conveying the photosensitivematerial A from the magazine to the image reading section 15. A cutter34 is disposed between the first and second roller pairs 32a and 32b tocut the photosensitive material A to a predetermined length. An exposingopening 36 formed in the bottom surface of the partition wallsurrounding the image reading section 15 is positioned between the thirdand fourth roller pairs 32c and 32d.

The thermal image developing section 17, which is surrounded with a heatinsulating partition wall 38, is disposed below the image readingsection 15. The photosensitive material A passed through the imagereading section is conveyed into the thermal image developing section 17through fifth and six roller pairs 32e and 32f. The section 17 includesa hollow-cylinder-shaped heating drum 44 accommodating a halogen lamp40, and an endless belt 46 which contacts a part of the outercylindrical wall of the heating drum 44 in such a manner that thephotosensitive material A is conveyed while being held between the beltand the drum and heated.

The photosensitive material A passed through the section 17 is deliveredthrough a seventh roller pair 32g to the sheet stacking section 19. Thesection 19 has a Y-shaped guide board 50. The board 50 has a firstincoming (receiving) path 52a near the seventh roller pair 32g, a secondincoming path 52b near an eighth roller pair 32h, and an outgoing(outlet) path 52c at which the first and second incoming paths meet andwhich is close to a ninth roller pair 32i.

A cassette 56 holding a number of image receiving sheets C is loaded inthe lower portion of the housing at one corner. In the apparatus of FIG.1, a sheet feeding roller 58 is installed above the cassette 56 tosupply the image receiving sheet C through the eighth roller pair 32hinto the second incoming path 52b of the Y-shaped guide board 50. Amanual sheet supplying inlet 60 is formed in the housing 12 above thecassette 56 so that the image receiving sheet C can be manually insertedinto the inlet 60 and delivered to the second incoming path 52b througha tenth roller pair 32j.

A pressurizing unit 66, including the pressure-operated imagetransferring section 21 and the sheet separating section 23, is providedbehind the ninth roller pair 32i. The pressurizing unit 66, as shown inFIGS. 2 and 3, includes first supporting boards 68a and 68b secured tothe housing 12, and second supporting boards 72a and 72b which arerotatably supported, at first ends, through shafts 70 by the boards 68aand 68b, respectively. A first pressurizing roller 74, which is rotatedby a drive source (not shown), is mounted on a shaft 76 which extendsbetween the first supporting boards 68a and 68b. A second pressurizingroller 80 is rotatably supported through a shaft 78 by the secondsupporting boards 72a and 72b. These pressurizing rollers 74 and 80 canbe manufactured by hardening a roller made of SK or SCM material by highfrequency hardening, and plating the cylindrical wall with hardchromium. Preferably, the hardening depth is at least 5 mm from theouter cylindrical wall of the roller, and the hardness is at least HRC60.

Holders 82a and 82b are formed at the end portions of the firstsupporting boards 68a and 68b which confront second ends of the secondsupporting boards 72a and 72b, respectively. Bolts 86a and 86b aresecured to the holders 82a and 82b through holes 84a and 84b formed inthe second end portions of the second supporting boards 72a and 72b,respectively. In this case, springs 90a and 90b are interposed betweenthe flanges of the bolts 86a and 86b and the second end portions of thesecond supporting boards 72a and 72b, respectively, so that the secondend portion of the second supporting boards 72a and 72b are urgedtowards the holders 82a and 82b of the first supporting boards 68a and68b, respectively. That is, the second pressurizing roller 80 is pushedagainst the first roller 74 by the elastic force of the springs 90a and90b.

First holding boards 94a and 94b are rotatably supported, at first ends,through shafts 92 by the first supporting boards 68a and 68b,respectively. A first back-up roller 96 is rotatably supported through ashaft 98 by the first holding boards 94a and 94b. The length l of theback-up roller 96 is determined from the following expression:

    l=ΔL±20 (mm)                                      (1)

where L is the length of the first pressurizing roller 74.

Bolts 104a and 104b are inserted into holes 102a and 102b formed insecond end portions of the first holding boards 94a and 94b, and aresecured to holders 100a and 100b formed on the first supporting boards68a and 68b, respectively. Springs 108a and 108b are interposed betweenthe flanges 106a and 106b of the bolts 104a and 104b and the second endportions of the first holding boards 94a and 94b, respectively, so thatthe second end portions of the first holding boards 94a and 94b areurged towards the holders 100a and 100b of the first supporting boards68a and 68b, respectively. As a result, the first back-up roller 96 ispushed against the back of the first pressurizing roller 74 at itsmiddle portion. A cleaning shoe 110 is mounted on mounting boards 112which are secured to the shafts 92 of the first holding boards 94 a and94b in such a manner that the shoe is in sliding contact with the firstpressurizing roller 74.

Similarly, second holding boards 116a and 116b are rotatably supported,at first end portions, through shafts 114 by the second supportingboards 72a and 72b, respectively. A second back-up roller 120 isrotatably supported through a shaft 118 by the second holding boards116a and 116b. Similar to the first back-up roller 96, the length of thesecond back-up roller 120 is determined so as to satisfy equation (1)above where, in this case, L is the length of the second pressurizingroller 80. The back-up rollers 96 and 120 are preferably made of thesame material as the pressurizing rollers 74 and 80.

Bolts 126a and 126b are inserted into holes 124a and 124b formed insecond end portions of the second holding boards 116a and 116b and arethen secured to holders 122a and 122b formed on the second supportingboards 72a and 72b, respectively. Springs 130a and 130b are interposedbetween the flanges 128a and 128b of the bolts 126a and 126b and thesecond end portions of the second holding boards 116a and 116b so thatthe second end portions of the second holding boards 116a and 116b areurged towards the holders 122a and 122b by the elastic forces of thesprings, and the second back-up roller 120 is pressed against the secondpressurizing roller 80 at its middle portion. A second cleaning shoe 132is coupled to mounting boards 134 which are mounted on the supportingshafts 114 of the second holding boards 116a and 116b in such a mannerthat the shoe is in sliding contact with the second pressurizing roller80.

A blade 136 is disposed between the ninth roller pair 32i and the secondpressurizing roller 80 and mounted in such a manner that it is rotatablewith respect to the first supporting boards 68a and 68b. The blade 136is provided with a spring 138. The spring 138 pulls the blade 136 at oneend so that the other end of the blade 136 is brought into slidingcontact with the second pressurizing roller 80. A guide board 140 isprovided for the blade 136 and mounted in such a manner as to confrontthe latter.

An eleventh roller pair 32k is supported by the first supporting boards68a and 68b. Guide boards 142 are provided between the eleventh rollerpair 32k and the first and second pressurizing rollers 74 and 84. Theguide boards form Y-shaped first and second outgoing paths 144a and 144bdownstream of the eleventh roller pair 32k. A sheet separating pawl 146with a sharp end 145 extending towards the eleventh roller pair 32k ismounted between the first and second outgoing paths 144a and 144b insuch a manner that it is rotatably supported between the firstsupporting boards 68a and 68b.

The first outgoing path 144a is coupled through twelfth throughfourteenth roller pairs 32l through 32n to a disposal tray 150positioned below the photosensitive material supplying section 13. Thephotosensitive materials A are delivered into the disposal tray 150. Onthe other hand, the second outgoing path 144b is connected throughfifteenth and sixteenth roller pairs 32o and 32p to a take-out tray 152.The image receiving sheets C are delivered into the tray 15. The fixingsection 25 employing ultraviolet lamps 154 is arranged between thefifteenth and sixteenth roller pairs 32o and 32p.

The image recording apparatus of the invention is arranged fundamentallyas described above. The operation of the image recording apparatus thusarranged will be described.

An original S bearing image data is placed on the original supportingglass plate 14, and then it together with the glass plate 14 is conveyedby a conveying device (not shown) as indicated by the arrow, i.e., it isauxiliarily scanned. In this operation, in the image reading section 15the light source 18 is turned on to emit a light beam which is appliedthrough the opening 16 and the glass plate 14 to the original S. On theother hand, a photosensitive material A is pulled out of the magazine 30loaded in the photosensitive material supplying section 13 and isconveyed by means of the first through fourth rollers pairs 32a through32d in such a manner that it is moved along the exposing opening 36 ofthe image reading section 15 at the same speed as the glass plate 14.

The light beam reflected from the image data of the original S isapplied through the opening 36 to the photosensitive material A in themain scanning direction by means of the focusing optical system 20. Asdescribed above, the photosensitive material A includes a photosensitivepressure-sensitive thermal developing type recording material layer. Thelatent image of the original is formed on the photosensitive material Aby the reflected light beam. The photosensitive material A pulled out ofthe magazine 30 is cut to a predetermined length by the cutter 34.

The photosensitive material A thus exposed is delivered to the thermalimage developing section 17 through the fifth and sixth roller pairs 32eand 32f. In the section 17, the photosensitive material A is conveyedwhile being held between the heating drum 44 and the endless belt 46.During this conveyance, the photosensitive material A is subjected tothermal developing by the halogen lamp 42. As a result, the polymerizingcompound in the region covered by the latent image is polymerized andthe microcapsules in that region are hardened.

Then, the photosensitive material A is delivered through the seventhroller pair 32g and via the first incoming path 52a of the Y-shapedguide board 50 to the sheet piling section 19. The cassette 56accommodating a number of image receiving sheets C is loaded in theimage recording apparatus 10. The image receiving sheets are delivered,one at a time, through the eighth roller pair 32h and the secondincoming path 52b of the Y-shaped guide board 50 to the sheet stackingsection 19 by means of the sheet feeding roller 58. As a result, in thesheet stacking section 19, the sheet C is brought into contact with thelower surface of the photosensitive material A. In this connection, itshould be noted that the sheet stacking state is adjusted so that, whenthe image receiving sheet C is stacked on the photosensitive material A,the front edge of the photosensitive material A is closer to the ninthroller pair 32i than the image receiving sheet C. The image receivingsheet C may be supplied through the manual sheet supplying inlet 60opening in one side of the housing 12 and through the tenth roller pair32j to the sheet stacking section 19 by the operator.

The photosensitive material A and the image receiving sheet C stackedtogether is delivered through the outgoing path 54 in the sheet stackingsection 19 to the pressure-operated image transferring section 21 bymeans of the ninth roller pair 32i. In the section 21, as shown in FIGS.2 and 3, the first and second pressurizing rollers 74 and 80 are pressedagainst each other by the elastic forces of the springs 90a and 90b, andthe photosensitive material A and the image receiving sheet C areintroduced into the nip region of the pressurizing rollers 74 and 80.Since the front edge of the blade 136 is abutted against the outercylindrical wall of the second pressurizing roller 80 by the spring 138,the photosensitive material A and the image receiving sheet C, whichhave been stacked together, are suitably introduced into the nip regionof the first and second pressurizing rollers 74 and 80.

When the photosensitive material A and the image receiving sheet C arepressed by the rollers 74 and 80, the microcapsules in the region of thephotosensitive material A where no latent image is formed are broken,and hence the color image forming material is transferred to the imagereceiving sheet C; that is, a visible image is formed on the sheet C.

As described above, the first and second pressurizing rollers 74 and 80are pressed against each other, at both ends, through the shafts 76 and78 by the elastic forces of the springs 90a and 90b, while the first andsecond back-up rollers 96 and 120 are pressed against the first andsecond pressurizing rollers 74 and 80, at the middle, through the shafts98 and 118 by means of the springs 108a and 108b and 130a and 130b,respectively. The length l of the first and second back-up rollers 96and 120 is set to one-third the length L of the first and secondpressurizing rollers 74 and 80, as shown in FIG. 3, so that thephotosensitive material A and the image receiving sheet C are pressedsuitably against each other.

In an actual example in which the length L of the first and secondpressurizing rollers 74 and 80 was set to 330 mm while the length l ofthe first and second back-up rollers 96 and 120 was set to 110 mm, thepressurizing force distribution was as indicated by the solid line inFIG. 4. Therefore, as is apparent by comparison with the broken line inFIG. 4 which shows the case where the first and second back-up rollers96 and 120 were not employed, the nonuniform pressurizing forcedistribution due to the bend of the first and second pressurizingrollers 74 and 80 was suitably corrected. Accordingly, the image dataformed, as the latent image, on the photosensitive material A isuniformly transferred to the image receiving sheet C with high accuracy.It is not always necessary for the ratio of the length L of the firstand second pressurizing rollers 74 and 80 to the length of the first andsecond back-up rollers 96 and 120 to be exactly 3:1. That is, it hasbeen confirmed through experiments that the length may, in the exampleunder discussion, vary within ±20 mm.

In addition, it is known that the relation between the pressurizingforce applied to the photosensitive material A and the image receivingsheet C and the density of the image transferred onto the imagereceiving sheet C is as shown in FIG. 5. That is, FIG. 5 shows that thedensity of the image transferred to the image receiving sheet Cincreases substantially in proportion to the pressurizing force appliedto the photosensitive material and the image receiving sheet. However,after the pressurizing force reaches a certain value, the density ismaintained substantially unchanged. Therefore, if the springs 90a, 90b,108a, 108b, 130a and 130b are adjusted according to the above-describedrelation, then the most suitable pressurizing force can be applied tothe photosensitive material A and the image receiving sheet. That is, ifthe elastic forces of these springs are adjusted so that thepressurizing force of the first and second pressurizing rollers 74 and80 is uniform in the longitudinal direction, then not only can the bestimage, free from unevenness, be obtained, but also image unevenness dueto nonuniformities in the material of the photosensitive material A andthe image receiving sheet C is eliminated, and in addition thephotosensitive material A and the image receiving sheet C can beconveyed straightly, without deviation from the designated conveyancepath, at all times.

The photosensitive material A and the image receiving sheet C which havebeen pressurized at the pressure-operated image transferring section 21,is delivered through the guide board 142 to the sheet separating section23 by means of the eleventh roller pair 32k. In the sheet separatingsection 23, the sheet separating pawl 146 is turned about the shaft 148in the direction of the arrow to separate the photosensitive material Afrom the image receiving sheet C. As described above, in the sheetstacking section 19, the photosensitive material A is stacked on theimage receiving sheet C in such a manner that the front edge of thephotosensitive material A is ahead of that of the image receiving sheetC. Therefore, the photosensitive material A is delivered to the firstoutgoing path 144a with the sharp end 145 of the sheet separating pawl146, while the image receiving sheet C separated from the photosensitivematerial A is delivered to the second outgoing path 144b.

The image receiving sheet C delivered to the second outgoing path 144bis passed to the fixing section 25 by means of the fifteenth roller pair32o, where the image transferred to the image receiving sheet C is fixedby means of the ultraviolet lamps 154. The sheet C thus processed isdelivered to the take-out tray 152 by means of the sixteenth roller pair32p. On the other hand, the photosensitive material A in the firstoutgoing path 144a is delivered to the disposal tray 150 by means of thetwelfth, thirteenth and fourteenth roller pairs 32l, 32m and 32n.

In a second embodiment, the first and second backup rollers 96 and 120pressed against the first and second pressurizing rollers 74 and 80 attheir middle portion are replaced by a pair of rollers 156a and 156b anda pair of rollers 158a and 158b, respectively, as shown in FIG. 6. Thatis, when the distance m between the pair of rollers 156a and 156b, whichis equal to that between the pair of rollers 158a and 158b, is madeequal to the length l of the first and second back-up rollers 96 and120, the resultant pressurizing force distribution is similar to thatshown in FIG. 4. In this case, the total weight of the rollers 156a,156b, 158a and 158b is smaller than that of the rollers 96 and 120, andtherefore the image recording apparatus can be reduced in weight.

As described above, the image recording apparatus of the invention isdesigned so that, after a latent image corresponding to the image dataof an original is formed on the photosensitive pressure-sensitive imagerecording material, the image receiving sheet is pressed against theimage recording material with the pressurizing rollers which arepressed, at their middle portions by the back-up rollers, respectively,whose length is about one-third the length of the pressurizing rollers,so that the image is accurately transferred to the image receivingsheet. In this operation, the pressurizing rollers press the imagerecording material and the image receiving sheet uniformly with the aidof the back-up rollers so that the image transferred to the imagereceiving sheet is considerably high in picture quality. Since thepressurizing rollers are pressed by back-up rollers having the mostappropriate configuration, a reduction in the weight of the imagerecording apparatus can be readily achieved. This is another merit ofthe invention.

A third embodiment of the invention will be described with reference toFIGS. 7 and 8.

In this embodiment, the first back-up roller 96 has a substantiallycylindrical middle portion having a length L of constant diameter, andright and left circular-truncated-cone-shaped portions which are taperedtowards the ends. The periphery of each of the junctions between thecylindrical middle portion and the right and leftcircular-truncated-cone-shaped portions is rounded with a radius ofcurvature of 50 mm or more.

The first and second pressurizing rollers 74 and 80 are pressed againsteach other at both ends through the shafts 76 and 78 by the elasticforces of the springs 90a and 90b, while the first and second back-uprollers 96 and 120 are pressed against the first and second pressurizingrollers 74 and 80, at their middle portions, through the shafts 98 and118 by means of the springs 108a and 108b and 130a and 130b,respectively. As a result, the first and second back-up rollers 96 and120 are slightly curved upwardly and downwardly by the elastic forces ofthe springs 108a and 108b and 130a and 130b, respectively. However,adjusting the elastic forces to suitable values can bring the side wallsof the cylindrical middle portions and the side walls of thecircular-truncated-cone-shaped right and left portions of the first andsecond back-up rollers, that is, the side walls of the first and secondback-up rollers 96 and 120, into contact with the backs of thepressurizing rollers 74 and 80, respectively. Thus, the photosensitivematerial A and the image receiving sheet C are suitably pressed againsteach other.

In this connection, it has been confirmed through experiments that, ifthe length of contact between the pressurizing roller and the back-uproller is at least 10 mm, the pressurizing rollers are prevented frombeing deformed, and the image data recorded on the photosensitivematerial A is uniformly and accurately transferred to the imagereceiving sheet C.

It will be evident to those skilled in the art that various changes andmodifications may be made also to this embodiment without departing fromthe invention. For instance, the back-up rollers may take the form ofcrown rolls which are larger in diameter towards the middle than the twoends.

In a fourth embodiment of the invention, the pressure applied to thephotosensitive material A and the image receiving sheet C is adjusted bycontrolling the elastic forces of the springs 90a, 90b, 108a, 108b, 130aand 130b so that, as shown in FIG. 9, it increases gradually from bothends of the pressurizing rollers 74 and 80 towards the middle.Accordingly, the photosensitive material A and the image receiving sheetC are pressed against each other forming no crease, and the image datais accurately transferred onto the image receiving sheet.

That is, when the photosensitive material A and the image receivingsheet C is held between the pressurizing rollers 74 and 80, both endportions thereof tend to displace towards the two ends of thepressurizing rollers 74 and 80 because the pressurizing force is smallerat the two ends of the pressurizing rollers 74 and 80. Therefore, evenif the photosensitive material A and/or the image receiving sheet C hascreases, the creases are smoothed out, as a result of which thephotosensitive material A and the image receiving sheet C are conveyedwhile being maintained in a highly flat state. Thus, the image datarecorded on the photosensitive material A is uniformly transferred tothe image receiving sheet C; that is, the resultant image on the sheet Cis high in picture quality.

In addition, as mentioned above, it is known that the relation betweenthe pressurizing force applied to the photosensitive material A and theimage receiving sheet C and the density of the image transferred to theimage receiving sheet C by the pressurizing force is as shown in FIG. 5.That is, FIG. 5 shows that the density of the image transferred to theimage receiving sheet C increases substantially in proportion to thepressurizing force applied to the photosensitive material and the imagereceiving sheet. However, after the pressurizing force reaches a certainvalue (about 500 kg/cm²), the density is maintained substantiallyunchanged. Therefore, if the springs 90a, 90b, 108a, 108b, 130a and 130bare adjusted according to the above-described relation, then the mostsuitable pressurizing force can be applied to the photosensitivematerial A and the image receiving sheet C. For instance, if the elasticforces of the springs are adjusted so that, as shown in FIG. 9, apressure of about 500 kg/cm² is applied to both ends of the pressurizingrollers 74 and 80, then the resultant image is best in quality with aminimum pressure, and the difficulty can be eliminated of the resultantimage not being uniform in density because of the nonuniformity inmaterial of the photosensitive material A and the image receiving sheetC. The pressurizing rollers 74 and 80 are used merely to provide apressure which is at least 500 kg/cm² and increases gradually from bothends thereof towards the middle. Therefore, it is unnecessary for thepressurizing rollers 74 and 80 to have a considerably high manufacturingaccuracy, and accordingly the rollers can be easily manufactured.

In accordance with a fifth embodiment of the invention, it has beenfound that, when the deviation a of the pressure distribution of thepressurizing rollers 74 and 80 in the axial direction thereof is setwithin a predetermined range as shown in FIG. 10, then the resultantimage is higher in picture quality. More specifically, it has been foundthat when the deviation a is held within 30%, the photosensitivematerial A and the image receiving sheet C are effectively preventedfrom being creased, and when the deviation is within 20%, the formationof creases is completely prevented, and accordingly the resultant imageis substantially or completely free from nonuniformities in density dueto the formation of creases. Accordingly, a very high picture quality isobtained. If, as described above, the deviation a of the pressuredistribution is held within 30%, it is unnecessary to manufacture thepressurizing rollers 74 and 80 with an extremely high accuracy; that is,these rollers can be inexpensively manufactured.

If the elastic forces of the springs 90a, 90b, 108a, 108b, 130a and 130bare adjusted so that the pressurizing force of the first and secondpressurizing rollers 74 and 80 is uniform in the longitudinal directionwithin the deviation l thereof, then not only can an image free fromunevenness be obtained, but also image unevenness due to nonuniformitiesin the material of the photosensitive material A and the image receivingsheet C can be eliminated, and in addition the photosensitive material Aand the image receiving sheet C can be conveyed straightly, i.e.,without meander, at all times.

As described above, in the image recording method of the fifthembodiment in which the photosensitive material is pressurized andconveyed by the pressurizing rollers in such a manner that, while thephotosensitive material passes through the pressurizing rollers, thepressure distribution of the pressurizing rollers in the longitudinaldirection is held within 30% in deviation from a constant value, thephotosensitive material will not be creased when pressurized by thepressurizing rollers, and therefore the resultant image is high inquality. Furthermore, since the pressure distribution of thepressurizing rollers is held within a deviation of 30%, the pressurizingrollers can be inexpensively manufactured.

As was described above with respect to FIGS. 7 and 8, the first andsecond pressurizing rollers 74 and 80 are pressed against each other atboth ends through the shafts 76 and 78 by the elastic forces of thesprings 90a and 90b, and are pushed by the elastic forces of the springs108a and 108b and the springs 130a and 130b through the shafts 98 and118 and the first and second back up rollers 96 and 120, respectively.Therefore, the first back-up roller 96 is slightly upwardly curved bythe elastic forces of the spring 108a and 108b, while the second back-uproller 120 is also slightly downwardly curved by the elastic forces ofthe springs 130a and 130b. However, in this case, if the elastic forcesof the springs are suitably adjusted, then the first and second back-uprollers 96 and 120 can be pushed against the first and secondpressurizing rollers 74 and 80 in such a manner that the side of thecylindrical middle portion and the sides of the right left taperedportions of each of the back-up rollers, that is, the entire sides ofthe back-up rollers are brought into contact with the respectivepressurizing rollers, whereby the photosensitive material A and theimage receiving sheet C are pressurized most suitably.

It has been found through experiments that, when the contact lengthbetween the pressurizing roller and the back-up roller is set to atleast 10 mm, the first and second pressurizing rollers 74 and 80 arefree from inward buckling so that the image data recorded on thephotosensitive material A is uniformly and accurately transferred to theimage receiving sheet C.

In accordance with the sixth embodiment, the dimensions of the first andsecond pressurizing rollers 74 and 80 and the first and second back-uprollers 96 and 120, and the spring constants of the springs 90a, 90b,108a, 108b, 130a and 130b are as indicated in the following Table 1. Inthis case, the maximum width of the photosensitive material A and theimage receiving sheet C which can pass through the first and secondpressurizing roller while being pressed is about 300 mm. Referencecharacters L₁, L₂, D₁, D₂ and D₃ in Table 1 are defined as indicated inFIGS. 7 and 8.

                  TABLE 1                                                         ______________________________________                                                  Pressurizing   Back-up rollers                                      Item      rollers 74 & 80                                                                              96 & 120                                             ______________________________________                                        Length    L.sub.1 = 330 mm                                                                             L.sub.2 = 350 mm                                                              Cylindrical middle                                                            portion's length                                                              l = 110 mm                                           Diameter  D.sub.1 = 40 mm                                                                              D.sub.2 = 40 mm                                                               D.sub.3 = 36 mm                                      Spring    Springs 90a and 90b                                                                          Springs 108a, 108b,                                  constant  15 kg/mm       130a and 130b                                                                 24.2 kg/mm                                           Spring    55.5 mm        25 mm                                                length                                                                        ______________________________________                                    

When, according to the data indicated in Table 1 above, the bolts 86a,86b, 104a, 104b, 126a and 126b were turned to suitably adjust theelastic forces of the springs 90a, 90b, 108a and 108b, 130a and 130b topress the photosensitive material A and the image receiving sheet C,which were 300 mm in width, with the first and second pressurizingrollers 74 and 80, the pressure applied to the sheets was distributed asshown in FIG. 11. That is, the pressure was about 500 kg/cmz at bothends, about 600 kg/cm² at the middle. In this case, the sheets were notcreased at all. Since a pressure of at least 500 kg/cm² was applied tothe sheets over the entire length, the resultant image was uniform indensity; that is, the image was satisfactorily transferred from thephotosensitive material A to the image receiving sheet C.

Similarly, photosensitive materials and image receiving sheets which are210 mm and 182 mm in width were tested. As a result, it has been foundthat they were not creased at all and the resultant images were high inpicture quality. In these tests, the drive torque for the drive device(not shown) for driving the first and second pressurizing rollers 74 and80 was 140 kg-cm.

In the above-described embodiment, the pressures of the back-up rollersare changed by adjusting the elastic forces of the springs; however,they may be changed by means of bolts as shown in FIGS. 12 and 13. Thatis, in the pressurizing unit 66 as shown in FIGS. 7 and 8, the springs108a, 108b, 130a and 130b are removed, and instead bolts 150a through150d are used as shown in FIGS. 12 and 13 so as to adjust the pressuresof the backup rollers 96 and 120.

In samples of the photosensitive material A and the image receivingsheet C 300 mm rollers 74 and 80 in the pressurizing unit thus modified,the pressure applied to the sheets was distributed as shown in FIG. 14.That is, the pressure was 500 kg/cm² at both ends and 900 kg/cm² at themiddle. Under this condition, the photosensitive materials A and theimage receiving sheets C 300 mm and 210 mm in width were pressurizedwith the first and second pressurizing rollers 74 and 80. However, thesesheets were not creased at all, and the resultant images weresatisfactory in picture quality.

As is apparent from the above description, the pressure applied to thephotosensitive material and the image receiving sheet in the case wherethe pressures of the back-up rollers are adjusted by means of the bolts(referred to as "bolt pressurization") is more variable than thatapplied to the photosensitive material and the image receiving sheet inthe case where the pressures of the back-up rollers are adjusted bymeans of the springs (referred to as "spring pressurization"). This isbecause the rigidity in the case of bolt pressurization is higher thanthat in the case of spring pressurization. Also, the drive torquerequired for the drive source (not shown) to turn the first and secondpressurizing rollers 74 and 80, being 200 kg-cm, is larger by 50% thanin the case of spring pressurization. However, a pressurizing unit usingbolt pressurization can be manufactured at a lower cost than one usingspring pressurization. Generally, bolt pressurization is preferablyemployed for an image recording apparatus produced on a small scale andspring pressurization for an image recording apparatus produced on alarge scale.

An image recording apparatus according to an eighth embodiment of theinvention, as shown in FIG. 15, has an original supporting glass plate202 mounted on a housing 201 in such a manner that it can slidablyreciprocate in directions indicated by the arrow A. That is, the glassplate 202 is reciprocated in the directions of the arrow A with thesurface of the original to be copied directed downwardly.

An illuminating lamp 208 with a reflecting mirror 206 for illuminatingthe original is provided below the glass plate 202. In addition, a fiberlens array 210 for forming the image of the original on a photosensitivematerial S at a predetermined position is also provided below the glassplate 202.

A photosensitive material cartridge 214, which accommodates a roll ofphotosensitive material 212 formed by winding the photosensitivematerial S, is detachably mounted on one side of the housing 201. A pairof photosensitive material supplying (feeding) rollers 221 and 222enclosed in a magazine-connected dark box 220 are provided at thephotosensitive material supplying outlet 216 of the magazine 214, sothat a predetermined length of the photosensitive material S of the roll212 is supplied when required and the material retracted when necessary.

When the front end of the photosensitive material S approaches thephotosensitive material supplying rollers 221 and 222, the two rollersmove away from each other (as indicated by phantom lines in the drawing)so as to facilitate the movement of the photosensitive material S. Acutter unit 223 for cutting the photosensitive material S and a guideboard 224 are provided forwardly of the dark box 220. ("Forwardly of" asused herein is intended to mean "downstream of" of the photosensitivematerial in the direction of movement.)

An exposed photosensitive material supporting roller 226 and twophotosensitive material nip rollers 228 and 230 abutted against thesupporting roller 226 are arranged downstream of the guide board 224.The photosensitive material S is guided by the guide board 224 andbrought into close contact with the roller 226 by action of the niprollers 228 and 230 so that the latent image is formed on thephotosensitive material S at the position 232 between the nip rollers228 and 230 by means of the fiber lens array 210.

An image developing device 240 for developing the latent image on thephotosensitive material S by heating is provided in front of the exposedphotosensitive material supporting roller 226. The image developingdevice 240 includes a developing housing 242 of the heat insulationtype, a heating roller 244 heated to about 120° C., an endless belt 250supported by four belt supporting rollers 246, 247, 248 and 249 andwound through an angle of about 270° C. around the heating roller 244,and a nip roller 252 held abutted against the supporting roller 249. Thecomponents 244, 246, 247, 248, 249, 250 and 252 are mounted in thedeveloping housing 242.

The developing device 240 is further composed of guide 254 for guidingthe photosensitive material S delivered from the exposed photosensitivematerial supporting roller 226 to the heating roller 244 and separatingthe developed photosensitive material S from the heating roller 244, avertical guide 258 for guiding to an outlet 256 the developedphotosensitive material S which is delivered by means of the beltsupporting roller 249 and the nip roller 252, and a sensor 260 fordetecting the front end of the photosensitive material S at the outlet256.

A sheet stacking device 270 for stacking the photosensitive material Sand the image receiving sheet one on another is provided just below theoutlet 256 of the image developing device 240. The device 270 includes apair of rollers 262 and 264 abutted against each other, a nip roller 266abutted against the roller 264, and a guide member 268 for guiding thephotosensitive material S delivered thereto to the nip region of therollers 262 and 264.

An image receiving-sheet supplying device 272 is provided beside thesheet stacking device 270. More specifically, an image-receiving-sheetcartridge 273, including a roll of image receiving sheet 271 rotatablysupported on a stand, is detachably mounted on the opposite side of thehousing 201. Inside the housing 201, a pair of sheet feeding rollers 274and 276, a cutter unit 277 and a guide board 278 are arranged beside thecartridge 273.

A pressure-operated image transfer device 288 is provided below thesheet stacking device 270. The device 288 is composed of a fixed niproller 282, a free nip roller 280, and a back-up roller 284 whose axisis flush with those of the nip rollers 280 and 282. The back-up roller284 is provided to make the pressure of the nip rollers 280 and 282uniform in the axial direction. The nip rollers 280 and 282 are pressedagainst each other at a pressure of about 500 kg/cm².

A sheet separating device 290 for separating the image receiving sheetfrom the photosensitive material is provided below the image transferdevice 288. The device 290 includes a guide member 92, a first conveyingroller 94, a second conveying roller 96, and a sheet separating belt 302laid over guide rollers 298 and 300 in such a manner that it pressesonly the photosensitive material S at both sides of the first conveyingroller 294.

A photosensitive material disposing section 304 is provided on one sideof the sheet separating device 290 and an image fixing device 306 on theother side. The photosensitive material disposing section 304 includes aguide member 308, a pair of conveying rollers 310 and 312, and adisposal box 314. In the photosensitive material disposing section 304,the photosensitive material delivered from the sheet separating device290 and guided by the guide member 308 is passed into the disposal box314 by means of the conveying rollers 310 and 312.

The image fixing device 306 is composed of a guide member 320 with anillumination opening 321, an ultraviolet lamp 324 with a reflectingmember 322, and a pair of conveying rollers 326 and 328. In the imagefixing device, ultraviolet rays are applied to the image receiving sheetC for about five seconds, the sheet C being delivered from the sheetseparating device 290 and guided by the guide member 320.

An image-receiving-sheet take-out section 307 is provided downstream ofthe image fixing device 306. The section 307 includes a take-out tray330 for receiving the image receiving sheet C. The tray 330 is connectedto the housing 301 in such a manner that it protrudes from the housing301.

The pressure-operated image transfer device of this embodiment of theinvention will be described with reference to FIG. 16 in more detail.

The fixed nip roller 282 is rotatably supported, at both ends, bybearings 336 provided on a base 331 secured to the device body. The freenip roller 280 is arranged parallel to the fixed nip roller 282, and itsdiameter D₂ is smaller than the diameter D₁ of the fixed nip roller 282.The two end portions of the free nip roller 280 are supported by guidemembers 333 in such a manner that the free nip roller 280 is movableonly in a direction perpendicular to the central axis of the fixed niproller 282. The fixed nip roller 282 is rotated by a drive device (notshown) so as to convey the photosensitive material and the imagereceiving sheet while pressing them in cooperation with the free niproller 280.

The back-up roller 284 is provided on one side of the free nip roller280, on the other side of which the fixed nip roller 282 is disposed.The back-up roller 284 has an effective back-up portion 334 at themiddle whose width L₃ (hereinafter referred to as an effective back-upwidth L₃ " when applicable) is smaller than the widths L₁ and L₂ of thenip rollers 282 and 280. The effective back-up portion 334 merges withtapered portions 335 at both ends. The back-up roller 284 is rotatablysupported by bearings 337 at both ends, the bearings being secured torespective supporting members 332.

The diameter D₂ of the free nip roller 280 is smaller than that D₁ ofthe fixed nip roller 282 since the back-up pressure is applied only fromthe side of the free nip roller 280. Therefore, the diameter of the freenip roller 280 is made smaller than that of the fixed nip roller 282 sothat the free nip roller 280 can be readily bent by the back-up roller284 and the fixed nip roller 282 can be also readily bent.

The reason why the effective back-up width L₃ of the back-up roller 284is smaller than the widths of the nip rollers 280 and 282 is that, in aback-up roller supported at both ends, the pressures at the two ends arehigher than that at the middle. In order to compensate the pressure atthe middle of the roller, the effective back-up width L₃ of the back-uproller 284 is made smaller.

The supporting members 332 are urged by means of spring members andbolts (not shown) provided on one side of the back-up roller 284, on theother side of which the free nip roller 280 is disposed, so as to pressthe back-up roller 284 at a predetermined pressure. As a result, theback-up roller 284 pushes the free nip roller 280, which in turn appliespressure to the fixed nip roller 282 so that the latter is presseduniformly over its length.

Several experiments were performed on the pressure-operated imagetransfer device thus constructed. In these experiments, a plurality offree nip rollers differing in diameter were used to transfer the imagefrom the photosensitive material to the image receiving sheet bypressurization, and the pressure distribution in the nip region wasmeasured. The results of the experiments are as indicated in Table 2 andFIGS. 17A through FIG. 17G.

                  TABLE 2                                                         ______________________________________                                                  Free nip roller                                                     Experiment                                                                              diameter (D.sub.2)                                                                            Result of transfer                                  ______________________________________                                        A         10 mm           Not uniform                                         B         15 mm           Not uniform                                         C         20 mm           Satisfactory                                        D         25 mm           Satisfactory                                        E         30 mm           Satisfactory                                        F         35 mm           Creased                                             G         40 mm           Creased                                             ______________________________________                                    

In all of the experiments described above, the width L₁ and diameter D₁of the fixed nip roller were set to 250 mm and 40 mm, respectively, andthe effective back-up width L₃ and diameter of the back-up roller wereset to 80 mm and 50 mm, respectively.

In experiments A and B, as is apparent from the pressure distributionsshown in FIGS. 17A and 17B, respectively, the pressure at the middle ofthe nip region was excessively high, as a result of which the image wasnot uniformly transferred to the image receiving sheet.

In experiments F and G, as is clear from FIGS. 17F and 17G,respectively, the pressures at both end portions of the nip region wereexcessively high, as a result of which the image receiving sheet wascreased.

Through these experiments, the most suitable dimensions of the rollers280, 282 and 284 have been confirmed as follows:

For the fixed nip roller, the width L₁ is 210 mm to 350 mm, and thediameter D₁ is 30 mm to 50 mm. For the free nip roller, the width L₂ isequal to or larger than the width L₁ (L₂ ≧L₁), and the diameter D₂ is ina range of D₁ /1.6 to D₁ /1.3. For the back-up roller, the effectiveback-up width L₃ is L₁ /3±10 mm, and the diameter is 30 mm to 50 mm ormore. Especially, the most suitable diameter of the free nip roller isin a range of 23 mm to 25 mm.

In the above-described embodiment, the spring members and bolts areemployed to adjust the pressurizing force of the back-up roller.However, the invention is not limited thereto or thereby; that is, theymay be replaced by other suitable pressurizing force adjusting elements.

While the above embodiment of the invention has been described withreference to an image recording apparatus in which the photosensitivematerial which is heated for developing the latent image formed thereonis stacked on the image receiving material, and the photosensitivematerial and the image receiving material are pressurized so that theimage is transferred to the image receiving material, the invention isnot limited thereto or thereby. That is, the technical concept of theinvention is applicable also to an apparatus such as anelectrophotographing device in which rollers are used to record images.

As is apparent from the above description, according to the invention,the pressure provided in the nip region of a pair of pressurizing niprollers arranged parallel to one another can be made uniform over theirlength by a single back-up roller, which makes it possible to reduce theweight and size of the pressure-operated image transfer device in theimage recording apparatus.

In the pressure-operated image transfer device of the invention, theforce of the pressurizing nip roller can be controlled merely byadjusting the pressurizing force of the back-up roller. Therefore, theforce adjusting mechanism is simple in construction. For the samereason, the pressure-operated image transfer device can handle a varietyof photosensitive materials or image receiving materials differing inthickness or in width.

Accordingly, the pressure-operated image transfer device of theinvention can provide images free from the difficulties that, because ofthe nonuniform pressurization, the image is not uniformly transferred tothe image receiving sheet and the resultant colors are not uniform.

While preferred embodiments of the invention have been described, it isbelieved evident to those skilled in the art that various changes andmodification may be made therein without departing from the invention.

What is claimed is:
 1. An image recording apparatus in which aphotosensitive pressure-sensitive image recording material and an imagereceiving material stacked together are pressurized with a pair ofpressurizing rollers while being held therebetween so that an image istransferred from said image recording material to said image receivingmaterial, in which the improvement comprises:a back-up roller forapplying a predetermined pressurizing force to at least one of said pairof pressurizing rollers at a middle portion thereof; and said back-uproller having a length which is substantially one-third of a length ofsaid pair of pressurizing rollers.
 2. The apparatus as claimed in claim1, in which said back-up roller comprises first and second rollersspaced apart from each other by a distance substantially one-third saidlength of said pair of pressurizing rollers.
 3. The apparatus as claimedin claim 1, in which the length of said back-up roller satisfies thefollowing equation:

    l=1/3L±20 (mm)

where L is the length of said pressurizing rollers.
 4. An imagerecording apparatus employing a photosensitive material formed bycoating a support with a material which, when pressurized, fixes animage formed thereon through optical exposure to obtain a visible imageby pressurization, comprising:a pair of pressurizing rollers forpressing said photosensitive material; a back-up roller abutted againstone of said pair of pressurizing rollers, said back-up roller comprisinga circular-cylinder-shaped middle portion and twocircular-truncated-cone-shaped end portions which extend from both endsof said circular-cylinder-shaped middle portion and are graduallytapered towards the ends of said back-up roller; and means for pressingsaid back-up roller against said pressurizing roller with apredetermined pressure.
 5. The image recording apparatus as claimed inclaim 4, wherein said pressing means comprises spring means.
 6. Theimage recording apparatus as claimed in claim 4, wherein said pressingmeans comprises adjustable bolt means.
 7. The image recording apparatusas claimed in claim 4, in which junctures of saidcircular-cylinder-shaped middle portion and said twocircular-truncated-cone-shaped end portions of said back-up roller arerounded with a radius of curvature of at least 50 mm.
 8. The imagerecording apparatus as claimed in claim 4, in which said back-up rolleris crown-roll shaped.
 9. The image recording apparatus as claimed inclaim 4, in which said pressurizing rollers and said back-up rollercomprise a roller made of a material selected from the group consistingof SK and SCM materials subjected to high frequency hardening and platedwith hard chromium.
 10. In an image recording apparatus in which aphotosensitive material formed by coating a support with a materialwhich, when pressurized, fixes an image formed thereon through opticalexposure is stacked on an image receiving material, and saidphotosensitive material and said image receiving material arepressurized to transfer said image thus fixed from said photosensitivematerial to said image receiving material, a pressure-operated imagetransferring device comprising:a fixed nip roller rotatably supportedwhich has a width L₁ in range of 210 mm to 350 mm and a diameter D₁ inrange of 30 mm to 50 mm; a free nip roller arranged parallel to saidfixed nip roller, said free nip roller having a width L₂ equal to orlarger than said width L₁ of said fixed nip roller and a diameter D₂ ina range of D₁ /1.6 to D₁ /1.3; and a back-up roller pushing said freenip roller against said fixed nip roller, said back-up roller having aneffective back-up width L₃ defined by the following equation:

    L.sub.3 =L.sub.1 /3±10 mm.


11. The image recording apparatus as claimed in claim 10, in which saidback-up roller has an effective back-up portion corresponding to saideffective back-up width L₃ at a middle portion thereof and two taperedportions merging with said effective back-up portion at both ends, saidboth ends being tapered towards the ends of said back-up roller.